问题积累—HibernateDaoSupport 类session未关闭导致的连接泄露问题

 

  HibernateDaoSupport 类session未关闭导致的连接泄露问题 收藏

Spring+Hibernate做项目, 发现有member在不加事务的情况下就去调用 getSession() 方法, 结果导致数据库连接不能释放, 也无法正常的提交事务(只能做查询, 不能做save(), update()). 如果配合连接池使用的话, 不出几分钟就会导致连接池无法拿到新连接的情况.

不过, 只要给DAO或者Service加入了事务, 就不会出现连接泄漏的问题.

谈谈解决方案:

最佳方案: 加入事务, 例如 tx 标签或者 @Transactional 都可以.

最笨方案: 修改代码, 使用 HibernateTemplate 来完成相关操作:

 

 public List queryAll( final String hql, final Object… args) {

              List list = getHibernateTemplate().executeFind( new HibernateCallback() {

                       public Object doInHibernate(Session session)

                       throws HibernateException, SQLException {

                      Query query = session.createQuery(hql);

                       for ( int i =0; i < args. length ; i++) {

                             query.setParameter(i, args[i]);

                      }

                      List list = query.list();

                       return list;

                      }

                     });

              return list;        

       }

       public Serializable save(Object entity) {

              return getHibernateTemplate().save(entity);

       }

 但是缺陷显而易见, 要有N多的代码要进行改动.

HibernateDaoSupport 代码里面的原始说明文档指出直接调用getSession()方法必须用配套的releaseSession(Session session)来释放连接, 根据我的测试, 就算配置了 OpenSessionInViewFilter(前提: 不加事务), 也不会关闭这个Session. 也许有人说可以用连接池, 这种情况和Db pool没关系, 用了pool就会发现连接很快就会满, 只会over的更快.  反过来, 如果不配置OpenSessionInViewFilter, 在DAO里提前用 releaseSession()关闭连接, 就可能会在JSP中出现Lazy载入异常. 另一个不配事务的问题就是无法更新或者插入数据. 下面就是原始的JavaDoc中的说明:

 

  /**

         * Obtain a Hibernate Session, either from the current transaction or

         * a new one. The latter is only allowed if the

         * {@link org.springframework.orm.hibernate3.HibernateTemplate#setAllowCreate “allowCreate”}

         * setting of this bean’s {@link #setHibernateTemplate HibernateTemplate} is “true”.

         * <p><b> Note that this is not meant to be invoked from HibernateTemplate code

         * but rather just in plain Hibernate code. </b> Either rely on a thread – bound

         * Session or use it in combination with {@link #releaseSession} .

         * <p> In general, it is recommended to use HibernateTemplate, either with

         * the provided convenience operations or with a custom HibernateCallback

         * that provides you with a Session to work on. HibernateTemplate will care

         * for all resource management and for proper exception conversion.

         * @return the Hibernate Session

         * @throws DataAccessResourceFailureException if the Session couldn’t be created

         * @throws IllegalStateException if no thread – bound Session found and allowCreate=false

         * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, boolean)

         */

       protected final Session getSession()

           throws DataAccessResourceFailureException, IllegalStateException {

              return getSession( this . hibernateTemplate .isAllowCreate());

       }

       /**

         * Close the given Hibernate Session, created via this DAO’s SessionFactory,

         * if it isn’t bound to the thread (i.e. isn’t a transactional Session).

         * <p> Typically used in plain Hibernate code, in combination with

         * {@link #getSession} and {@link #convertHibernateAccessException} .

         * @param session the Session to close

         * @see org.springframework.orm.hibernate3.SessionFactoryUtils#releaseSession

         */

       protected final void releaseSession(Session session) {

              SessionFactoryUtils.releaseSession(session, getSessionFactory());

       }

 

不需要改原始代码的最终方案(方案三):

不过, 如果项目里已经有了大量直接调用getSession()而且没有加入事务配置的代码(如历史原因导致), 这些代码太多, 没法一一修改, 那就最好寻求其它方案, 最好是不需要修改原来的Java代码的方案. 我采用的这第三个方案是重写 HibernateDaoSupport用ThreadLocal保存Session列表并编写一个配套的过滤器来显式关闭Session, 并在关闭之前尝试提交事务. 下面是重写的 HibernateDaoSupport 代码:

 

package org.springframework.orm.hibernate3.support;

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.List;

import org.hibernate.HibernateException;
import org.hibernate.Session;
import org.hibernate.SessionFactory;

import org.springframework.dao.DataAccessException;
import org.springframework.dao.DataAccessResourceFailureException;
import org.springframework.dao.support.DaoSupport;
import org.springframework.orm.hibernate3.HibernateTemplate;
import org.springframework.orm.hibernate3.SessionFactoryUtils;

/**
 * 修改后的避免连接泄漏的 HibernateDaoSupport, 多连接版本, 不保证跨DAO的事务.
 *
 */
publicabstractclass HibernateDaoSupport extends DaoSupport {
/** 使用 ThreadLocal 保存打开的 Session 列表 */
privatestaticfinal ThreadLocal< List<Session> > sessions = new ThreadLocal< List<Session> >();

/**
     * 获取Hibernate连接.
     * @return
     */
publicstatic List<Session> getSessionList() {
//1. 先看看是否有了List get()
        List list = sessions.get();
// 2. 没有的话从创建一个, put()
if(list == null) {
            list = new ArrayList();
            sessions.set(list);
        }
// 3. 返回 Session
return list;
    }

/**
     * 关闭当前线程中未正常释放的 Session.
     */
publicstaticvoid closeSessionList() {
//        1. 先看看是否有了List get()
        List<Session> list = sessions.get();
// 2. 有的话就直接关闭
if(list != null) {
            System.out.println(SimpleDateFormat.getDateTimeInstance().format(new java.util.Date()) +
" -------- 即将释放未正常关闭的 Session");

for(Session session : list) {
                System.out.println("正在关闭 session =" + session.hashCode());
// ! 关闭前事务提交
if(session.isOpen()) {
try {
                        session.getTransaction().commit();
                    } catch(Exception ex) {
try {
                            session.getTransaction().rollback();
                        } catch (HibernateException e) {
// TODO Auto-generated catch block
//e.printStackTrace();
                        }
                    }
try {
                        session.close();
                    } catch(Exception ex) {

                    }

                }
//releaseSession(session); // 无法调用
            }
            sessions.remove();
        }

    }

private HibernateTemplate hibernateTemplate;

/**
     * Set the Hibernate SessionFactory to be used by this DAO.
     * Will automatically create a HibernateTemplate for the given SessionFactory.
     * @see #createHibernateTemplate
     * @see #setHibernateTemplate
     */
publicfinalvoid setSessionFactory(SessionFactory sessionFactory) {
if (this.hibernateTemplate == null || sessionFactory != this.hibernateTemplate.getSessionFactory()) {
this.hibernateTemplate = createHibernateTemplate(sessionFactory);
        }
    }

/**
     * Create a HibernateTemplate for the given SessionFactory.
     * Only invoked if populating the DAO with a SessionFactory reference!
     * <p>Can be overridden in subclasses to provide a HibernateTemplate instance
     * with different configuration, or a custom HibernateTemplate subclass.
     * @param sessionFactory the Hibernate SessionFactory to create a HibernateTemplate for
     * @return the new HibernateTemplate instance
     * @see #setSessionFactory
     */
protected HibernateTemplate createHibernateTemplate(SessionFactory sessionFactory) {
returnnew HibernateTemplate(sessionFactory);
    }

/**
     * Return the Hibernate SessionFactory used by this DAO.
     */
publicfinal SessionFactory getSessionFactory() {
return (this.hibernateTemplate != null ? this.hibernateTemplate.getSessionFactory() : null);
    }

/**
     * Set the HibernateTemplate for this DAO explicitly,
     * as an alternative to specifying a SessionFactory.
     * @see #setSessionFactory
     */
publicfinalvoid setHibernateTemplate(HibernateTemplate hibernateTemplate) {
this.hibernateTemplate = hibernateTemplate;
    }

/**
     * Return the HibernateTemplate for this DAO,
     * pre-initialized with the SessionFactory or set explicitly.
     * <p><b>Note: The returned HibernateTemplate is a shared instance.</b>
     * You may introspect its configuration, but not modify the configuration
     * (other than from within an {@link #initDao} implementation).
     * Consider creating a custom HibernateTemplate instance via
     * <code>new HibernateTemplate(getSessionFactory())</code>, in which
     * case you're allowed to customize the settings on the resulting instance.
     */
publicfinal HibernateTemplate getHibernateTemplate() {
returnthis.hibernateTemplate;
    }

protectedfinalvoid checkDaoConfig() {
if (this.hibernateTemplate == null) {
thrownew IllegalArgumentException("'sessionFactory' or 'hibernateTemplate' is required");
        }
    }

/**
     * Obtain a Hibernate Session, either from the current transaction or
     * a new one. The latter is only allowed if the
     * {@link org.springframework.orm.hibernate3.HibernateTemplate#setAllowCreate "allowCreate"}
     * setting of this bean's {@link #setHibernateTemplate HibernateTemplate} is "true".
     * <p><b>Note that this is not meant to be invoked from HibernateTemplate code
     * but rather just in plain Hibernate code.</b> Either rely on a thread-bound
     * Session or use it in combination with {@link #releaseSession}.
     * <p>In general, it is recommended to use HibernateTemplate, either with
     * the provided convenience operations or with a custom HibernateCallback
     * that provides you with a Session to work on. HibernateTemplate will care
     * for all resource management and for proper exception conversion.
     * @return the Hibernate Session
     * @throws DataAccessResourceFailureException if the Session couldn't be created
     * @throws IllegalStateException if no thread-bound Session found and allowCreate=false
     * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, boolean)
     */
protectedfinal Session getSession()
throws DataAccessResourceFailureException, IllegalStateException {
        Session session = getSession(this.hibernateTemplate.isAllowCreate());

// 开始事务
try {
            session.beginTransaction();
        } catch (HibernateException e) {
            e.printStackTrace();
        }

        getSessionList().add(session);

return session;
    }

/**
     * Obtain a Hibernate Session, either from the current transaction or
     * a new one. The latter is only allowed if "allowCreate" is true.
     * <p><b>Note that this is not meant to be invoked from HibernateTemplate code
     * but rather just in plain Hibernate code.</b> Either rely on a thread-bound
     * Session or use it in combination with {@link #releaseSession}.
     * <p>In general, it is recommended to use
     * {@link #getHibernateTemplate() HibernateTemplate}, either with
     * the provided convenience operations or with a custom
     * {@link org.springframework.orm.hibernate3.HibernateCallback} that
     * provides you with a Session to work on. HibernateTemplate will care
     * for all resource management and for proper exception conversion.
     * @param allowCreate if a non-transactional Session should be created when no
     * transactional Session can be found for the current thread
     * @return the Hibernate Session
     * @throws DataAccessResourceFailureException if the Session couldn't be created
     * @throws IllegalStateException if no thread-bound Session found and allowCreate=false
     * @see org.springframework.orm.hibernate3.SessionFactoryUtils#getSession(SessionFactory, boolean)
     */
protectedfinal Session getSession(boolean allowCreate)
throws DataAccessResourceFailureException, IllegalStateException {

return  (!allowCreate ?
            SessionFactoryUtils.getSession(getSessionFactory(), false) :
                SessionFactoryUtils.getSession(
                        getSessionFactory(),
this.hibernateTemplate.getEntityInterceptor(),
this.hibernateTemplate.getJdbcExceptionTranslator()));
    }

/**
     * Convert the given HibernateException to an appropriate exception from the
     * <code>org.springframework.dao</code> hierarchy. Will automatically detect
     * wrapped SQLExceptions and convert them accordingly.
     * <p>Delegates to the
     * {@link org.springframework.orm.hibernate3.HibernateTemplate#convertHibernateAccessException}
     * method of this DAO's HibernateTemplate.
     * <p>Typically used in plain Hibernate code, in combination with
     * {@link #getSession} and {@link #releaseSession}.
     * @param ex HibernateException that occured
     * @return the corresponding DataAccessException instance
     * @see org.springframework.orm.hibernate3.SessionFactoryUtils#convertHibernateAccessException
     */
protectedfinal DataAccessException convertHibernateAccessException(HibernateException ex) {
returnthis.hibernateTemplate.convertHibernateAccessException(ex);
    }

/**
     * Close the given Hibernate Session, created via this DAO's SessionFactory,
     * if it isn't bound to the thread (i.e. isn't a transactional Session).
     * <p>Typically used in plain Hibernate code, in combination with
     * {@link #getSession} and {@link #convertHibernateAccessException}.
     * @param session the Session to close
     * @see org.springframework.orm.hibernate3.SessionFactoryUtils#releaseSession
     */
protectedfinalvoid releaseSession(Session session) {
        SessionFactoryUtils.releaseSession(session, getSessionFactory());
    }

}

 

 

用这个类来覆盖Spring内置的那个HibernateDaoSupport, 然后随便编写一个过滤器, 如下所示:

 

 

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException {
    		req.setCharacterEncoding(this.charset);
    		chain.doFilter(req, res);
    		// 关闭遗漏的 Session
    		HibernateDaoSupport.closeSessionList();
}

 

 

 

把这个过滤器配置在过滤器链的第一个,　就OK了.

最后也许会有人说, 为什么不用tx标签在Spring中来配置一个通配符就全部加入了事务了呢? 不过很遗憾, 经测试发现此方式无法实现跨DAO的Hibernate事务, 所以只好很无奈的放弃了这种方式.

配置事务管理:http://www.blogjava.net/robbie/archive/2009/04/05/264003.html

原帖:http://yhkyo.com/archives/196